Differences In Tissue Susceptibility Research Articles

Peranan Sekuen Susceptibility Weight Imaging (SWI) Pada Pemeriksaan MRI Brain Pada Kasus Tumor

The aim of the research is to find out the role of the transverse suspectibility weighted imaging (SWI) sequence in brain MRI examination techniques in tumor cases. The research method used in this research is a qualitative descriptive study that uses a literature study approach to explore, analyze and identify information about how the Susceptibility Weighted Imaging (SWI) sequence plays a role in the Brain MRI examination process in patients who have tumors. The results and discussion of the literature review show: 1) Susceptibility-Weighted Imaging (SWI) on MRI brain has an important role in detecting blood degradation products, calcification and iron accumulation in glioblastoma. SWI allows visualization of small blood vessels, detection of iron, as well as identification of areas of calcification within the tumor, providing a more detailed picture of the nature and malignancy of glioblastoma. The Intratumoral Susceptibility Signal (ITSS) on SWI images is a visual marker associated with microhemorrhage, neoangiogenesis, and calcification, enabling tumor grading based on the frequency and distribution of these signals. In addition, Intralesional Susceptibility Signal (ILSS) also has an important role in differentiating glioblastoma from abscesses and metastases, with high levels of ILSS tending to be associated with tumor severity. Thus, the integration of SWI and ITSS and ILSS analysis can make a significant contribution to the characterization and assessment of the level of malignancy. 2) Susceptibility-Weighted Imaging (SWI) in the diagnosis of glioblastoma has the advantage of providing internal visualization of the tumor with high resolution. SWI is highly sensitive to differences in tissue susceptibility, allows the detection of neovascularization, hemorrhage, and calcification within glioblastoma, and provides detailed information about cerebral vascular anatomy. The advantages of SWI include its ability to image the Intratumoral Susceptibility Signal (ITSS) and Intralesional Susceptibility Signal (ILSS) and increase the visibility of low signal intensity structures. However, its shortcomings, namely sensitivity to artifacts, dependence on susceptibility phenomena, and subjective interpretation are aspects that need to be considered.

Quantitative Susceptibility Mapping in Cognitive Decline: A Review of Technical Aspects and Applications

In the human brain, essential iron molecules for proper neurological functioning exist in transferrin \((tf)\) and ferritin \((Fe3+)\) forms. However, its unusual increment manifests iron overload, which reacts with hydrogen peroxide. This reaction will generate hydroxyl radicals, and iron’s higher oxidation states. Furthermore, this reaction causes tissue damage or cognitive decline in the brain and also leads to neurodegenerative diseases. The susceptibility difference due to iron overload within the volume of interest (VOI) responsible for field perturbation of MRI and can benefit in estimating the neural disorder. The quantitative susceptibility mapping (QSM) technique can estimate susceptibility alteration and assist in quantifying the local tissue susceptibility differences. It has attracted many researchers and clinicians to diagnose and detect neural disorders such as Parkinson’s, Alzheimer’s, multiple sclerosis, and aging. The paper presents a systematic review illustrating QSM fundamentals and its processing steps, including phase unwrapping, background field removal, and susceptibility inversion. Using QSM, the present work delivers novel predictive biomarkers for various neural disorders. It can strengthen new researchers’ fundamental knowledge and provides insight into its applicability for cognitive decline disclosure. The paper discusses the future scope of QSM processing stages and their applications in identifying new biomarkers for neural disorders.

Investigation of the magnetic susceptibility properties of fresh and fixed mouse heart, liver, skeletal muscle and brain tissue.

Several magnetic resonance imaging (MRI) techniques exploit the difference in magnetic susceptibilities between tissues, but systematic measurements of tissue susceptibility are lacking. Furthermore, there is the question as to whether chemical fixation that is used for ex vivo MRI studies, affects the magnetic properties of the tissue. Here, we determined the magnetic susceptibility and water content of fresh and chemically fixed mouse tissue. Mass susceptibility of brain, heart, liver and skeletal muscle samples were determined on a vibrating sample magnetometer at room temperature. Measurements at 50, 125, 200 and 295K were performed to assess the temperature dependence of susceptibility. Moreover, we measured water content of fresh and fixed samples. All samples show mass susceptibilities between -0.068 and -1.929×10-8 m3/kg, compared to -9.338×10-9 m3/kg of double distilled water. Heart tissue has a more diamagnetic susceptibility than the other tissues. Compared to fresh tissue, fixed tissue has a less diamagnetic susceptibility. Fixed tissue was not different in water content to fresh tissue and showed no consistent dependence of susceptibility with temperature, whereas fresh tissue shows a decrease to at least 125K, indicative of a paramagnetic component. Biological tissues are diamagnetic in comparison to water, where the heart is more diamagnetic than the other tissues, with paramagnetic contributions. Fixation rendered tissue less diamagnetic compared to fresh tissue. Our measurements revealed differences in tissue susceptibility between VSM and QSM, inviting more research to compare susceptibility-based MRI methods with physical measurements of tissue susceptibility.

Tissue localization of piscidin host-defense peptides during striped bass (Morone saxatilis) development

Infectious diseases are a major cause of larval mortality in finfish aquaculture. Understanding ontogeny of the fish immune system and thus developmental timing of protective immune tissues and cells, may help to decrease serious losses of larval fishes when they are particularly vulnerable to infection. One component of the innate immune system of fishes is the host-defense peptides, which include the piscidins. Piscidins are small, amphipathic, α-helical peptides with a broad-spectrum of action against viral, bacterial, fungal, and protozoan pathogens. We describe for the first time the cellular and tissue localization of three different piscidins (1, 3, and 4) during striped bass (Morone saxatilis) larval ontogeny using immunofluorescent histochemistry. From 16 days post hatch to 12 months of age, piscidin staining was observed in cells of the epithelial tissues of gill, digestive tract, and skin, mainly in mast cells. Staining was also seen in presumptive hematopoietic cells in the head kidney. The three piscidins showed variable cellular and tissue staining patterns, possibly relating to differences in tissue susceptibility or pathogen specificity. This furthers our observation that the piscidins are not a monolithic family of antimicrobials, but that different AMPs have different (more specialized) functions. Furthermore, no immunofluorescent staining of piscidins was observed in post-vitellogenic oocytes, embryos, or larvae from hatch to 14 days post hatch, indicating that this critical component of the innate immune system is inactive in pre-hatch and young larval striped bass.

Clinical validation of susceptibility-weighted cardiovascular magnetic resonance in comparison to T2 and T2* imaging for detection of intramyocardial hemorrhage following acute myocardial infarction

Background Intramyocardial hemorrhage (IMH) identified by CMR is an established prognostic marker following acute myocardial infarction (AMI), but remains relatively underused in the clinical setting. Detection of IMH by T2-weighted or T2* CMR can be limited by long breath hold times and sensitivity to artefacts, especially at 3 Tesla. Alternative methods that can detect IMH with shorter breath hold times are therefore desirable. CMR is capable of detecting differences in the magnetic susceptibility of tissues. The paramagnetic properties of hemoglobin products within IMH cause local phase shifts relative to surrounding tissue. Phase data can be filtered and combined with magnitude data to generate susceptibility weighted MR images (SW MRI). SW imaging has been shown to be highly sensitive for the detection of cerebral hemorrhage, but typically uses long echo times, resulting in prolonged image acquisition. With the larger size of IMH, we hypothesized that SW MRI may be used with shorter echo times, leading to rapid imaging with breath hold times of approximately 4 seconds. We compared the image quality and diagnostic ability of this SW MRI pulse sequence with T2-weighted and T2* CMR to detect IMH at 3T. Methods

Zoomed EPI-DWI of the Pancreas Using Two-Dimensional Spatially-Selective Radiofrequency Excitation Pulses

BackgroundImplementation of DWI in the abdomen is challenging due to artifacts, particularly those arising from differences in tissue susceptibility. Two-dimensional, spatially-selective radiofrequency (RF) excitation pulses for single-shot echo-planar imaging (EPI) combined with a reduction in the FOV in the phase-encoding direction (i.e. zooming) leads to a decreased number of k-space acquisition lines, significantly shortening the EPI echo train and potentially susceptibility artifacts.PurposeTo assess the feasibility and image quality of a zoomed diffusion-weighted EPI (z-EPI) sequence in MR imaging of the pancreas. The approach is compared to conventional single-shot EPI (c-EPI).Material and Methods23 patients who had undergone an MRI study of the abdomen were included in this retrospective study. Examinations were performed on a 3T whole-body MR system (Magnetom Skyra, Siemens) equipped with a two-channel fully dynamic parallel transmit array (TimTX TrueShape, Siemens). The acquired sequences consisted of a conventional EPI DWI of the abdomen and a zoomed EPI DWI of the pancreas. For z-EPI, the standard sinc excitation was replaced with a two-dimensional spatially-selective RF pulse using an echo-planar transmit trajectory. Images were evaluated with regard to image blur, respiratory motion artifacts, diagnostic confidence, delineation of the pancreas, and overall scan preference. Additionally ADC values of the pancreatic head, body, and tail were calculated and compared between sequences.ResultsThe pancreas was better delineated in every case (23/23) with z-EPI versus c-EPI. In every case (23/23), both readers preferred z-EPI overall to c-EPI. With z-EPI there was statistically significantly less image blur (p<0.0001) and respiratory motion artifact compared to c-EPI (p<0.0001). Diagnostic confidence was statistically significantly better with z-EPI (p<0.0001). No statistically significant differences in calculated ADC values were observed between the two sequences.ConclusionZoomed diffusion-weighted EPI leads to substantial image quality improvements with reduction of susceptibility artifacts in pancreatic DWI.

Diffusion weighted inner volume imaging of lumbar disks based on turbo-STEAM acquisition

A magnetic resonance imaging (MRI) technique for diffusion weighted imaging (DWI) is described which, in contrast to echo planar imaging (EPI), is insensitive to off-resonance effects caused by tissue susceptibility differences, magnetic field inhomogeneities, or chemical shifts. The sequence combines a diffusion weighted (DW) spin-echo preparation and a stimulated echo acquisition mode (STEAM) module. Inner volume imaging (IVI) allows reduced rectangular field-of-view (FoV) in the phase encode direction, while suppressing aliasing artifacts that are usually the consequence of reduced FoVs. Sagittal turbo-STEAM images of the lumbar spine were acquired at 3.0 T with 2.0 × 2.0 mm 2 in-plane resolution and 7 mm slice thickness with acquisition times of 407 ms per image. To calculate the apparent diffusion coefficient (ADC) in lumbar intervertebral disks (IVDs), the DW gradients were applied in three orthogonal gradient directions with b-values of 0 and 300 s/mm 2. For initial assessment of the ADC of normal and abnormal IVDs a pilot study with 8 subjects was performed. Mean ADC values of all normal IVDs were (2.27 ± 0.40) × 10 −3 mm 2 /s and (1.89 ± 0.34) × 10 −3 mm 2/s for turbo-STEAM IVI and SE-EPI acquisition, respectively. Corresponding mean ADC values, averaged over all abnormal disks, were (1.93 ± 0.39) × 10 −3 mm 2/s and (1.51 ± 0.46) × 10 −3 mm 2/s, respectively, indicating a substantial ADC decrease ( p < 0.001).

Quantitative imaging of intrinsic magnetic tissue properties using MRI signal phase: An approach to in vivo brain iron metabolism?

Quantitative susceptibility mapping (QSM) based on gradient echo (GRE) magnetic resonance phase data is a novel technique for non-invasive assessment of magnetic tissue susceptibility differences. The method is expected to be an important means to determine iron distributions in vivo and may, thus, be instrumental for elucidating the physiological role of iron and disease-related iron concentration changes associated with various neurological and psychiatric disorders. This study introduces a framework for QSM and demonstrates calculation of reproducible and orientation-independent susceptibility maps from GRE data acquired at 3T. The potential of these susceptibility maps to perform anatomical imaging is investigated, as well as the ability to measure the venous blood oxygen saturation level in large vessels, and to assess the local tissue iron concentration. In order to take into account diamagnetic susceptibility contributions induced by myelin, a correction scheme for susceptibility based iron estimation is demonstrated. The findings suggest that susceptibility contrast, and therewith also phase contrast, are not only linked to the storage iron concentration but are also significantly influenced by other sources such as myelin. After myelin correction the linear dependence between magnetic susceptibilities and previously published iron concentrations from post mortem studies was significantly improved. Finally, a comparison between susceptibility maps and processed phase images indicated that caution should be exercised when drawing conclusions about iron concentrations when directly assessing processed phase information.

Chemical shift imaging in the head and neck at 3T: Initial results

To determine the optimal method to correct air and tissue susceptibility differences in the head and neck to allow proton ((1)H) chemical shift imaging (CSI) to be performed at 3T. Shimming protocols (iterative, first-order, and second-order) and perfluorocarbon (PFC) pads were evaluated using water peak linewidth measurements obtained from single-voxel magnetic resonance spectroscopy (MRS) on a head and neck phantom. After optimization of the technique, CSI was then tested on 14 patients with head and neck tumors. Second-order shimming (water peak linewidth, 4.6 Hz) performed significantly (P < 0.001) better than first-order (16.5 Hz) and iterative shimming (18 Hz) and the water peak linewidth was significantly reduced using PFC pads (P < 0.001). Using second-order shimming and PFC pads, CSI was successful in 10 patients with nodal metastases (n = 8) and benign tumors (n = 2) and unsuccessful in four patients with primary tumors along the aerodigestive tract. Proton CSI can be successfully performed in the head and neck using second-order shimming and PFC pads to correct air and tissue susceptibility differences. CSI was more successfully performed on nodal metastases, while CSI for primary tumors along the aerodigestive tract remains a challenge.

The contribution of chemical exchange to MRI frequency shifts in brain tissue

Recent high-field MRI studies based on resonance frequency contrast have revealed brain structure with unprecedented detail. Although subtle magnetic susceptibility variations caused by iron and myelin seem to be important to this contrast, recent research on protein solutions suggests that chemical exchange between water and macromolecular protons may contribute substantially to the observed gray-white matter frequency contrast. To investigate this, we performed spectroscopic MRI experiments at 14 T on samples of fixed human visual cortex and fresh pig brain. To allow direct observation of any exchange-induced frequency shifts, these samples were soaked in reference chemicals (TSP and dioxane) that are assumed not to be involved in exchange. For both fresh and fixed tissues and with both reference chemicals, substantial negative exchange-induced gray-white matter frequency contrast (-6.3 to -13.5 ppb) was found, whereas intracortical contrast was negligible. The sign of the gray-white matter exchange-induced frequency difference was opposite to the overall gray-white matter frequency difference observed in vivo. This suggests that exchange contributes to, but is not sufficient to explain, the frequency contrast in vivo and tissue susceptibility differences may have a greater contribution than previously thought. The exchange-dependent contribution may report on tissue chemical composition and pH.

Influence of lead acetate on glutathione and its related enzymes in different regions of rat brain

This study is intended to determine the effect of lead acetate on glutathione and its associated enzymes of rat brain. Wistar male rats were treated with lead acetate (500 ppm) through drinking water for a period of 8 weeks and parallel controls were maintained. They were sacrificed at the first, fourth and eighth week to isolate whole brains, which were separated into cerebellum, hippocampus, frontal cortex and brain stem. The data indicate enhanced (P < 0.05) glutathione peroxidase (G-Px) activity at most of the intervals for cerebellum, frontal cortex and brain stem, suggesting conversion of GSH to GSSG, while the hippocampus showed decreased levels. In contrast, glutathione reductase (GR) decreased significantly (P < 0.05) in cerebellum, frontal cortex and brain stem at all intervals except the fourth week in frontal cortex and brain stem. Hippocampus exhibited a gradual and significant (P < 0.05) increase in GR activity. Glutathione-S-transferase (GSTase) activity increased with exposure time in all four brain tissues, showing protection against lead acetate toxicity. The GSH and GSSG levels correlated well with the activities of GPx, GR and GSTase in all four regions of the brain. Overall the results indicate that lead acetate affects glutathione-related enzymes differentially and these changes can be attributed to differences in tissue susceptibility.

Biliary and Pancreatic Dysgenesis in Mice Harboring a Mutation in Pkhd1

Autosomal recessive polycystic kidney disease is a hereditary fibrocystic disease that involves the kidneys and the biliary tract. Mutations in the PKHD1 gene are responsible for typical forms of autosomal recessive polycystic kidney disease. We have generated a mouse model with targeted mutation of Pkhd1 by disrupting exon 4, resulting in a mutant transcript with deletion of 66 codons and expression at approximately 30% of wild-type levels. Pkhd1(del4/del4) mice develop intrahepatic bile duct proliferation with progressive cyst formation and associated periportal fibrosis. In addition, these mice exhibit extrahepatic manifestations, including pancreatic cysts, splenomegaly, and common bile duct dilation. The kidneys are unaffected both histologically and functionally. Fibrocystin is expressed in the apical membranes and cilia of bile ducts and distal nephron segments but is absent from the proximal tubule. This pattern is unchanged in orthologous models of autosomal dominant polycystic kidney disease due to mutation in Pkd1 or Pkd2. Mutant fibrocystin in Pkhd1(del4/del4) mice also retains this expression pattern. The hypomorphic Pkhd1(del4/del4) mouse model provides evidence that reduced functional levels of fibrocystin are sufficient for cystogenesis and fibrosis in the liver and pancreas, but not the kidney, and supports the hypothesis of species-dependent differences in susceptibility of tissues to Pkhd1 mutations.

Sensitivity and performance time in MRI dephasing artifact reduction methods.

Although shimming can improve static field inhomogeneity, local field imperfections induced by tissue susceptibility differences cannot be completely corrected and can cause substantial signal loss in gradient echo images through intravoxel dephasing. Dephasing increases with voxel size so that one simple method of reducing the effect is to use thin slices. Signal-to-noise ratio (SNR) can then be increased by averaging over the subslices to form the final, thick slice. We call this method subslice averaging or SSAVE. Alternatively, a range of different amplitude slice select rephase gradients can be used to compensate for different susceptibility induced gradient offsets. The final image can then be formed by combining individual images in a variety of ways: summation, summation of the squares of the images, forming the maximum intensity projection of the image set, and Fourier transformation followed by summation. We show here that, contrary to previous claims, the theoretical sensitivity (i.e., SNR divided by the square root of the imaging time) of all these alternative methods is very similar. However, performance time (i.e., minimum-imaging time) of the simplest method, SSAVE, is much shorter than that of alternatives. This is confirmed experimentally on phantoms and anesthetized mice. Magn Reson Med 45:470-476, 2001.

Diffusion-weighted single-shot line scan imaging of the human brain.

Single-shot line scan imaging (LSI) was adapted to diffusion-weighted (DW) MRI by replacing the initial 90 degrees radiofrequency pulse of the underlying high-speed stimulated echo sequence by a DW spin-echo preparation period. Implementation on a 2. 0 T whole-body MRI system yielded DW images of the human brain with b factors of 750 s mm(-2) and total imaging times of about 500 ms either for a single slice at 1.5 x 3.0 x 6 mm(3) resolution or simultaneously for up to seven slices at 3.75 x 3.75 x 8 mm(3) resolution. Isotropic DW images and maps of the trace of the diffusion tensor were calculated from four scans with different combinations of three orthogonal diffusion gradients. DW LSI combines high speed with robustness against image artifacts caused by motion (no phase ghosting) and tissue susceptibility differences (no signal losses, no geometric distortions). Because the latter is an important advantage over echo-planar imaging, DW LSI may find useful applications despite a limited signal-to-noise ratio. Magn Reson Med 42:772-778, 1999.

Magnetic resonance imaging of leaves

SUMMARYSeveral aspects of leaf anatomy and morphology make it difficult to image leaves with magnetic resonance imaging. Since most fully expanded leaves contain much intercellular air space and are often thin in one plane, relatively few water protons are available to provide signal. Their heterogeneous structure and the presence of many air‐water interfaces cause imaging problems as a result of differences in magnetic susceptibility of tissues and cells. Significant progress has been made in overcoming these difficulties, primarily by greatly reducing the echo time, permitting in vivo imaging of leaves at 7 and 9.4 Tesla with an in‐plane resolution of less than 15 μm2. Examples are shown and the potential for gaining information regarding in vivo water relations of leaves is discussed.

Congenital Methylmalonic Aciduria-Homocystinuria With Megaloblastic Anemia: Observations on Response to Hydroxocobalamin and on the Effect of Homocysteine and Methionine on the Deoxyuridine Suppression Test

Congenital methylmalonic aciduria-homocystinuria, a disorder with an incompletely defined cobalamin abnormality, has not been accompanied by megaloblastosis in most of the initially described cases. This has raised questions about the exact role of cobalamin in relation to megaloblastic anemia. Therefore, we present our observations on a patient with this syndrome whose manifestations conformed to current concepts of cobalamin function and on her response to hydroxocobalamin. In addition to the megaloblastic anemia (and other hematologic abnormalities) she developed severe neurologic impairment shortly after birth. Hydroxocobalamin injections diminished her methylmalonic acid and homocys-tine excretion and corrected her megaloblastosis, though mild neutrophil nuclear hypersegmentation has persisted even after a year. Clinical status also improved, particularly physical growth and neurologic development. However, she remains neurologically impaired following an unexplained clinical catastrophe. We documented her megaloblastic process by demonstrating abnormal deoxyuridine suppression test results in her initial bone marrow aspirate and normal results after treatment. Furthermore, the abnormal deoxyuridine suppression was corrected in vitro by folic acid, but not by methyltetrahydrofolic acid, cyanocobalamin, adenosylcobalamin, methylcobalamin, or methionine. Homocysteine slightly worsened the deoxyuridine suppression pattern. Subsequent studies showed that, in contrast to previous reports, homocysteine had no beneficial effect in other normoblastic or megaloblastic marrows either. The findings in our patient are compatible with the “methyltetrahydrofolate trap” hypothesis. Why this syndrome presents such a wide spectrum of manifestations is not entirely clear, nor is it clear why it should differ so from other disorders of cobalamin. These aspects are reviewed. Severity of the defect, differences in tissue susceptibility, or possibly even other factors such as ability to retain cobalamin intracellularly may influence the manifestations of this metabolic disorder.

Differences in susceptibility of tissues to revascularization studied in ectopic implants.

The survival rate of implanted marrow is reduced when the tissue is transferred from one site to another within the first 24 hours but not more than 48 hours after the initial implantation. Splenic implants can be transferred at any time after implantation without affecting the survival rate. The observation suggests a difference in the sensitivity of the two tissues to the avascular period that they experience prior to initiation of angiogenesis.

Susceptibility to estrogen of breast, vagina, and endometrium of various strains of mice.

In ovariectomized mice of strains with different mammary cancer incidence (C57. Dba, A), injected with equal amounts of alpha estradiol benzoate, the response of mammary gland, vagina and endometrium respectively varied in degree: Mice of strain C57 showed less mammary stimulation than mice of strains Dba or A. The vaginal epithelium was most sensitive in mice of strain C57, slower in responding in mice of strain Dba, and least responsive in mice of strain A. The endometrium reacted most vigorously in mice of strain C57, and less actively in strains Dba and A. Differences in the mammary cancer incidence of the strains examined are considered to be due to differences in tissue susceptibility rather than to genetic differences in the output of estrogen.